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        <p>The following vocabularies are essential, because they describe… vocabularies. Let’s get meta for a moment.</p>

<h1 id="-rdf"><a id="rdf"></a> RDF</h1>

<h2 id="prefix-and-namespace">Prefix and namespace</h2>
<ul>
  <li>rdf: http://www.w3.org/1999/02/22-rdf-syntax-ns#</li>
</ul>

<h2 id="description">Description</h2>

<p>RDF and RDFS are the foundation on which all other vocabularies are built. They enable the description of a graph of <a href="http://www.w3.org/2000/01/rdf-schema#Resource">rdfs:Resources</a>, each identified by an IRI.</p>

<p>RDF graphs are based on the notion of <a href="http://www.w3.org/1999/02/22-rdf-syntax-ns#Statement">rdf:statement</a>: a statement can be compared to a very simple sentence &lt;subject, verb, complement&gt;, e.g. <code class="highlighter-rouge">Charlie is a Person</code>. In the RDF terminology, we say that an <a href="http://www.w3.org/1999/02/22-rdf-syntax-ns#Statement">rdf:statement</a> has an <a href="http://www.w3.org/1999/02/22-rdf-syntax-ns#subject">rdf:subject</a> (the resource the statement is about), an <a href="http://www.w3.org/1999/02/22-rdf-syntax-ns#property">rdf:property</a> (the verb of the sentence, defining a characteristic of the subject) and an <a href="http://www.w3.org/1999/02/22-rdf-syntax-ns#object">rdf:object</a> (the value for the property for the subject). Therefore, the sentence <code class="highlighter-rouge">Charlie is a Person</code> could be expressed in RDF as <code class="highlighter-rouge">[ex](http://example.org/ns#):Charlie rdf:type [ex](http://example.org/ns#):Person</code>, where <code class="highlighter-rouge">&lt;http://example.org/ns#Charlie&gt;</code> is the subject, <code class="highlighter-rouge">rdf:type</code> the property, and <code class="highlighter-rouge">&lt;http://example.org/ns#Person&gt;</code> the object. Subject and predicate are necessarily individuals identified with an IRI, while the object is either an individual with an IRI, or a literal with a value (e.g. string or int).</p>

<h2 id="main-concepts">Main concepts</h2>

<ul>
  <li>Typing a Resource: <code class="highlighter-rouge">&lt;resource IRI&gt; rdf:type &lt;type IRI&gt;</code>, where the type is an <a href="http://www.w3.org/2000/01/rdf-schema#Class">rdfs:class</a></li>
</ul>

<h1 id="-rdfs"><a id="rdfs"></a> RDFS</h1>

<h2 id="prefix-and-namespace-1">Prefix and namespace</h2>
<ul>
  <li>rdfs: http://www.w3.org/2000/01/rdf-schema#</li>
</ul>

<h2 id="description-1">Description</h2>

<p>RDFS enables to build hierarchies of concepts by introducing the notion of <a href="http://www.w3.org/2000/01/rdf-schema#Class">rdfs:class</a>, and the <a href="http://www.w3.org/2000/01/rdf-schema#subClassOf">rdfs:subClassOf</a> property. Similarly, <a href="http://www.w3.org/1999/02/22-rdf-syntax-ns#Property">rdf:properties</a> can be organized hierarchically by using the <a href="http://www.w3.org/2000/01/rdf-schema#subPropertyOf">rdfs:subPropertyOf</a> property. RDFS also enables describing the types that can be attached to <a href="http://www.w3.org/2000/01/rdf-schema#Resource">rdfs:resources</a> when they are associated with an <a href="http://www.w3.org/1999/02/22-rdf-syntax-ns#Property">rdf:property</a> by specifying the property’s <a href="http://www.w3.org/2000/01/rdf-schema#domain">rdfs:domain</a> (the type of its subject) and <a href="http://www.w3.org/2000/01/rdf-schema#range">rdfs:range</a> (the type of the object). For instance, let’s imagine <code class="highlighter-rouge">ex:hasAuthor</code>, a property expressing the fact that someone is the author of a book. If we state that <code class="highlighter-rouge">ex:hasAuthor rdfs:domain ex:Book</code> and that <code class="highlighter-rouge">ex:hasAuthor rdfs:range ex:Person</code>, effectively what we say is that anytime we find a statement such as <code class="highlighter-rouge">ex:aBook ex:hasAuthor ex:someone</code>, we know that <code class="highlighter-rouge">ex:aBook</code> is of type <code class="highlighter-rouge">ex:Book</code>, and that <code class="highlighter-rouge">ex:someone</code> is a <code class="highlighter-rouge">ex:Person</code></p>

<h2 id="main-concepts-1">Main concepts</h2>

<ul>
  <li>Subclassing: <code class="highlighter-rouge">&lt;subclass IRI&gt; rdfs:subClassOf &lt;class IRI&gt;</code></li>
  <li>Specifying a property’s domain: <code class="highlighter-rouge">&lt;property IRI&gt; rdfs:domain &lt;type IRI&gt;</code></li>
  <li>Specifying a property’s range: <code class="highlighter-rouge">&lt;property IRI&gt; rdfs:range &lt;type IRI&gt;</code></li>
  <li>Adding a human-readable name to a concept identified by an IRI: <code class="highlighter-rouge">&lt;IRI&gt; rdfs:label "Some name"</code></li>
  <li>Adding a longer comment describing a concept: <code class="highlighter-rouge">&lt;IRI&gt; rdfs:comment "Some comment"</code></li>
  <li>Redirecting to another information source: <code class="highlighter-rouge">&lt;IRI&gt; rdfs:seeAlso &lt;IRI&gt;</code></li>
</ul>

<h1 id="-owl"><a id="owl"></a> OWL</h1>

<p><a href="/for-developers/apps/vocabularies/well-known">Back to the vocabularies index</a></p>

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